The invention relates to a display device having a display robe provided with a display screen and a tube neck located opposite thereto, and including a convergence correction device which comprises an arrangement of correction coils arranged around the neck, and a convergence correction circuit for applying correction currents to the correction coils.
U.S. Pat. No. 4,027,219 describes a device in which eight or twelve coils (solenoids) wound on cores of a ferromagnetic material are arranged in a row around the robe in such a way that their axes are coplanar, while they are incorporated in a circuit having controllable current sources in such a way that, upon energization, two four-pole fields and two six-pole fields are generated whose intensity and polarity are controllable for obtaining (static) convergence.
Drawbacks of the use of such a configuration of solenoids are:
the insensitivity, requiring a convergence circuit with relatively expensive amplifiers; PA1 little freedom of design as regards the exact field shape; PA1 a complicated electric circuit is required to generate all desired multipolar fields with a limited number of coils; PA1 less suitable for dynamic convergence due to the large inductance of the solenoids.